This invention relates generally to a device for measuring the rotation of a rotating element and, more particularly, to a device which has an encoder element that is carried by the rotating element and that cooperates with a sensor unit connected to a stationary element.
Conventionally, devices for measuring the angular position or speed of a rotating element include a sensor unit; immobile with respect to a measuring reference frame, cooperating with an encoder put in rotation by the rotating element, to provide a signal to an electronic processing center. A disadvantage of this type of device is that the active surface of the encoder facing the sensor, which is most often a multipolar magnetic surface or a surface with regularly spaced perforations possibly covered with a plastic or rubber-type protective film, is particularly sensitive to deposits of all sorts, possibly leading to disturbances of the generated signal. In particular, during the operation of such devices in an unfavorable environment, contaminating particles can adhere by projection or by magnetic attraction to the encoder.
A known approach to remedy this disadvantage is to enclose the encoder in a sealed enclosure in order to prevent the introduction of contaminating particles during operation. An example of this type of device is described and illustrated in the document EP-A-0 675 364 filed by The Timken Company. However, that proposed solution leads to the realization of a device which is complex and expensive to produce and does not make it possible to eliminate contaminating particles from depositing on the encoder during the phase of assembling the device in workshops.
Also proposed, as described and illustrated in the French patent application FR-A-2 730 566 filed by SKF, is a magnetic encoder device for a speed sensor in which the magnetic encoder is attached to a protective element. However, the thickness of the protective element increases the air gap between the magnetic encoder and the sensor and reduces the quality of the magnetic field received by the sensor, which makes the device more sensitive to exterior disturbances and reduces its range of operation.
The foregoing illustrates limitations known to exist in present devices and methods. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.